The present invention relates to a method of maintaining data service continuity in broadband (wideband) wireless (radio) access systems, in particular, to a method of establishing IP addresses of a mobile station for maintaining data service continuity during handover or in idle mode.
In general, in a broadband wireless (radio) access system, an idle mode for a mobile (or fixed) terminal (e.g., mobile station, mobile subscriber station (MSS), user terminal, user equipment (UE), etc.) is supported in order to minimize power consumption. In idle mode, a ‘paging zone’ is defined as the entire region that is handled by a plurality of bases station called a ‘paging group’ and all base station included within the same paging zone have the same paging cycle value (Paging_Cycle) and paging offset value (Paging_Offset).
The terminal may request to the base station for changing into idle mode, and the base station delivers its paging zone identification (Paging-group ID) and the paging cycle and paging offset associated thereto to the terminal to allow that terminal to change into idle mode state. During the idle mode, the terminal can determine whether to maintain or end its idle mode based upon the paging that is delivered in broadcast format from the base station at each paging period.
Additionally, when there is traffic (e.g., data, packets, etc.) that needs to be delivered by the terminal in idle mode, the terminal may end its idle mode at any time. Also, when a terminal in idle mode does not receive paging within a set period of time due to reasons such as moving into another paging zone, losing synchronization, etc., then the terminal ends its idle mode.
Hereafter, the procedures of a terminal transitioning into idle mode and a related art method of establishing an IP address when downlink data exists will be explained.
However in FIG. 1, a method of delivering downlink traffic (data) received by the terminal to a registered base station (BS), namely, from a previous base station (Serving BS) to a new base station (Target BS), is not defined in the related art. Also, even if a method of delivering data between base stations is defined, when the terminal re-establishes an IP address, the delivered data would be useless from the point of view of an application program in the terminal.
For example, in FIG. 1, if a terminal in idle mode moves into a paging zone and is within a zone of another base station BS#3, when downlink data arrives at the base station BS#1 that performed registration release for initially transitioning to the idle mode, the base station BS#3 informs the terminal to perform network entry through a paging message.
Then the data needs to be delivered from the base station BS#1 of which the terminal initially transitioned into idle mode to the base station BS#3 that currently received paging, but the related art does not define a method of such delivery.
Also, even if the above described problem is resolved, as shown in FIG. 2, in the related art, because the terminal performs IP address establishment (or re-establishment) upon receiving paging when there is downlink traffic (data), the received data is useless from the point of view of the terminal.
Accordingly, among the above-described operations in the related art, when there is traffic (data) that needs to be delivered to the terminal in idle mode, a method of receiving data without the terminal performing the IP establishment procedures is not defined.
Meanwhile, when performing handover in a broadband wireless access system, the terminal releases the connection with the base station that is in service (Serving BS), and performs handover to the targeted base station (Target BS) to which handover is to be made. When the terminal performs handover, a mobile terminal handover indicator (MOB_HO_IND) is delivered to the Serving BS, and if the handover indicator type (HO_IND_type) value is ‘00’, this means that the Serving BS is released (Serving BS Release).
In the related art, if the handover indicator type (HO_IND_type) value is ‘00’, Serving BS releases all connections and the state machine of the medium control layer (MAC) related to the terminal and the MAC PDUs (Protocol Data Units) can be ignored. Also, it is defined that the Serving BS can deliver the MAC state machine and MAC PDUs to the target base station (Target BS) for service continuity, or may be ignored by a request through a backbone message of the target base station. However, the particular operations that need to be performed for the terminal to receive such have not yet been specified.
Accordingly, the present invention defines the operations for receiving data delivered by the previous base station to the target base station after the terminal has moved.
FIGS. 3 and 4 depict two examples of performing handover by a mobile terminal. As shown in FIGS. 3 and 4, in the handover procedures according to a request of the terminal or a request of the base station, after the terminal performs initialization procedures for handover, a handover indicator (e.g., a MOB_HO_Indication) is transmitted to the base station (Serving BS) that is currently receiving service, and the relationship (connection) with the base station BS#1 receiving the service is released. Thereafter, the remaining procedures for accessing the target base station BS#3, namely, raging procedures and initial network entry, are performed by the terminal.
FIG. 5 depicts a format of a handover indicator (MOB_HO_Indication). When releasing the relationship (connection) with the base station BS#1 receiving service, the HO-IND-type is set as ‘00’.
However, as in the idle mode of the related art, if the serving base station delivers data to the target base station when the terminal performs handover, if the terminal that moved re-establishes the IP address during data reception, the received data become useless. Namely, as shown in FIG. 2, regardless of whether there is data being delivered after handover, the terminal immediately performs IP address establishment, and even if the delivered data is sent to the terminal, such data is useless from the point of view of the application program in the terminal. Thus, in such case, the time when IP address establishment should be performed needs to be clearly defined, but the related art fails to do so.